Polyacrylate esters, their preparation and use as a low-temperature flow-improver in middle distillate oils

ABSTRACT

A polymer having structural units derived from an ester ( 1 ) of an aliphatic carboxylic acid with an aliphatic alcohol, wherein either the acid or the alcohol is ethylenically unsaturated and the other of the acid or alcohol has a medium length chain group of 440 carbon atoms; said polymer having a molecular weight of less than 30,000.

[0001] The present invention relates to polymers, especially ester polymers, and to their preparation and use, particularly in diesel fuels.

[0002] Diesel fuels are middle distillates, generally boiling within the range of 170 to 390° C. Such fuels comprise hydrocarbons of varying types and molecular weights. Typically, 5 to 30% of the fuel consists of paraffinic hydrocarbons. Paraffinic hydrocarbons tend to have limited solubility. Thus, when the fuel is cooled, the less soluble, higher molecular weight paraffins tend to come out of solution as waxy crystals. The temperature at which this occurs is known as the cloud point of the fuel.

[0003] The waxy crystals formed at the cloud point have a strong affinity for each other and readily interlock to form larger crystal agglomerates. Thus, if the fuel is cooled further, more wax will come out of solution until there is sufficient to form an interlocking structure. Such structures may impede or prevent the flow of fuel through, for example, fuel lines and filters, causing operating difficulties in diesel fuel systems, particularly, during the winter, when ambient temperatures are low.

[0004] We have now developed a polymer which may be added to middle distillate oils to reduce the tendency for wax to deposit from such oils.

[0005] According to the present invention, there is provided a polymer having structural units derived from an ester (1) of an aliphatic carboxylic acid with all aliphatic alcohol, wherein either the acid or the alcohol is ethylenically unsaturated and the other of the acid or alcohol has a medium length chain group of 4-40 carbon atoms; said polymer having a molecular weight of less than 30,000.

[0006] The medium chain length group is preferably of 4 to 30 carbon atoms, more preferably, 6 to 25 carbon atoms, even more preferably, 10 to 22 carbon atoms, preferably 6-15, more preferably, 9-14 carbons, for example, 12 carbons.

[0007] Preferably, the molecular weight of the polymer is less than 25,000, for example, less than 20,000, preferably, less than 15,000 and more preferably, less than 10,000. In fact, the M_(w) of the polymer may be between 80 and 8,000; preferably, between 700 and 5000. In a preferred embodiment, the molecular weight is between 1800 and 3500.

[0008] Preferably also, the molecular weight distribution (Mw/Mn) is 2-20, for example, 2-6.

[0009] The polymer may be such that at least 10%, for example, at least 30%, for example, 35 to 45% of the aliphatic groups have said medium length chain group of 4 to 40 carbon atoms.

[0010] Ester (1) may be derived from an ethylenically unsaturated carboxylic acid, and a medium length chain alcohol. The unsaturated group of the ethylenically unsaturated carboxylic acid may be alpha, beta or gamma to the carboxylic group. The ethylenically unsaturated carboxylic acid may contain 3 to 15, for example, 3 to 10 carbon atoms, and is especially an aliphatic alpha ethylenically unsaturated carboxylic acid of formula CH₂═CRCO₂H, wherein R is hydrogen or an alkyl group of 1-3 carbons, for example, methyl, ethyl or propyl. Acrylic acids, and in particular, methacrylic acids are preferred. The acid may also be a mono, di or tricarboxylic acid. Suitable diacids include fumaric, maleic and crotonic acids.

[0011] The medium length alcohol is preferably linear, but may be branched. The alcohol contains 4-40 carbon atoms, preferably, 4 to 30, more preferably, 6 to 25 carbon atoms, even more preferably, 10 to 22 carbon atoms. Suitable alcohols may contain 8, 10, 12, 14, 16, 18, 20 or 22 carbon atoms. Thus, suitable alcohols include octanol, decanol, dodecanol, tetradecanol, hexadecanol, octadecanol, eicosanol, docosanol and nafol. Branched alcohols such as, for example, 2-methyl dodecyl alcohol are also suitable. The alcohol may be natural or synthesised, for example, by oxo or ALFOL processes.

[0012] The alcohols employed may be substantially pure, but are preferably mixtures of alcohols. Examples of such mixtures include natural lauryl alcohols and mixtures of alkanols of even carbon number, with one carbon number predominating with decreasing proportions of alkanols of lower and higher carbon number, as in e.g. a Gaussian distribution. Such mixtures may contain at least 50%, for example, at least 80 or 90% (by mole) of one alkanol. Examples of such mixtures are commercially produced lauryl alcohol with a majority of a 12 carbon alkanol and smaller amounts of 8, 10 and 14 carbon alkanols. Commercial mixtures of at least two of, for example, 8, 10, 12, 14, 16, 18, 20 or 22 carbon alcohols may be used.

[0013] The medium length chain aliphatic alcohol may also be employed as a mixture of alcohols with a bimodal distribution of the carbon number content, e.g. with at least 25% moles of each of 2 alcohols, especially alcohols different in at least 1, or at least 3 carbons, such as 1-6 e.g. 2 or especially 3-6 e.g. 4 or 6 carbons. Examples of such mixtures are 8 and 12, or 10 and 14 or 8 and 14 carbon alkanols.

[0014] In a preferred embodiment, ester (1) is an acrylate of an alcohol selected from the group consisting of: 1-octanol, 1-decanol, 1-dodecanol, 1-tetradecanol, 1-hexadecanol, 1-octadecaol, 1-eicosanol, and 1-docosanol. Preferably, no more than two alcohols are selected from said group. Where two alcohols are selected, they preferably have carbon numbers which differ by two.

[0015] Ester (1) may also be derived from an ethylenically unsaturated alcohol and a medium length chain carboxylic acid. The unsaturated group of the ethylenically unsaturated alcohol may be alpha, beta or gamma to the alcohol group. The ethylenically unsaturated alcohol preferably contains 2 to 6 carbon atoms. It may be an allyl alcohol, a methallyl alcohol, or a vinyl alcohol. The alcohol may be linear, as in for example, CH₂═CHOH. Alternatively, the alcohol may be branched, for example, as in methyl vinyl alcohol.

[0016] The medium length carboxylic acid is preferably linear, but may be branched. The acid is preferably saturated and may contain 4 to 40 carbons, for example, preferably, 4 to 30, more preferably, 6 to 25 carbon atoms, even more preferably, 10 to 22 carbon atoms. Suitable acids may comprise 8, 10, 12, 14, 16, 18, 20, or 22 carbon atoms Examples of suitable acid are n-octanoic, n-decanoic, n-undecanoic, n-dodecanoic, n-tridecanoic, n-tetradecanoic acids.

[0017] The acids may be substantially pure, but are preferably mixtures of acids, for example, as in lauric acid or mixtures of acids of even carbon number with one carbon number predominating with decreasing proportions of acids of lower and higher carbon numbers, as in e.g. a Gaussian distribution. Such mixtures may contain at least 50%, for example, at least 80 or 90% (by mole) of one alkanoic acid and smaller amount(s) of other alkanoic acid(s). Examples of such mixtures are commercial lauric acid consisting predominantly of acids having 12 carbon atoms. Small amounts of acids comprising 10 and 14 carbon atoms are also present.

[0018] The acid may also be used as a mixture of acids with a bimodal distribution of the carbon number content.

[0019] In addition to structural units derived from ester (1), the polymer may also comprise structural units derived from an ester (2). Ester (2) is different to ester (1), but falls within the same definition as ester (1). Thus, ester (2) is an ester of an aliphatic carboxylic acid with an aliphatic alcohol, wherein either the acid or the alcohol is ethylenically unsaturated and the other of the acid or alcohol has a medium length chain group of 4-40 carbon atoms.

[0020] Where ester (1) is derived from an ethylenically unsaturated carboxylic acid, and a medium length chain alcohol, ester (2) is also derived from an ethylenically unsaturated carboxylic acid, and a medium length chain alcohol. Where ester (1) is derived from an ethylenically unsaturated alcohol, and a medium length chain carboxylic acid, ester (2) is also derived from an ethyleneically unsaturated alcohol, and a medium length chain carboxylic acid.

[0021] In addition to structural units derived from ester (1), and optionally, ester (2), the polymer of the present invention may also comprise structural units derived from an ester (3). Ester (3) is an ester of an aliphatic carboxylic acid and an aliphatic alcohol, wherein either the acid or the alcohol is ethylenically unsaturated and the other of the acid or alcohol has a short chain aliphatic group of 1-4 carbon atoms. Where present, units derived from ester (3) may form 10 to 60 ml %, preferably, 20 to 40 mol % of the resulting polymer.

[0022] Where ester (1) is derived from an ethylenically unsaturated carboxylic acid, and a medium length chain alcohol, ester (3) is derived from an ethyleneically unsaturated carboxylic acid and an aliphatic alcohol of 1 to 4 carbon atoms. Suitable alcohols include methanol, ethanol. propanol and butanol. Methanol and t-butanol are preferred

[0023] Where ester (1) is derived from an ethyleneically unsaturated alcohol, and a medium length chain carboxylic acid, ester (3) is derived from an ethylenically unsaturated alcohol and a carboxylic acid of 1 to 4 carbon atoms. Suitable acids include formic acid, acetic acid, propaionic acid and buytyric acid. Acetic acid and propionic acid are preferred.

[0024] The polymers of the invention may also contain structural units from other unsaturated monomers e.g. ones monomers containing at least one N and/or S atom or O atom in an ether linkage.

[0025] The polymers of the present invention may be obtained by direct polymerisation of ester (1), optionally, with ester (2) and/or (3). For example, for polymers comprising structural units derived from esters (1), and (2) and/or (3), the constituent ester monomers may be co-polymerised together directly.

[0026] The polymerisation may be performed in a conventional manner with or without a diluent. Where a diluent is required, a hydrocarbon diluent, such as hexane, heptane, or a higher boiling hydrocarbon oil may be employed.

[0027] The polymerisation may be carried out at a temperature of 25-120° C., such as 60-100° C. Optionally, a free radical catalyst, such as a peroxide or an azo catalyst may be employed. Suitable free radical catalysts include benzoyl peroxide. A suitable azo catalyst is azobis isobutyronitrile.

[0028] The polymerisation is usually performed under inert conditions, for example, under nitrogen or argon. The polymerisation time may be 0.5-40 hr, preferably 5-25 hr, at a reaction temperature of 60-100° C. At the end of the polymerisation, the reaction product may be purified by evaporation under vacuum to remove unreacted monomer, and/or precipitation of the product with methanol from a liquid aromatic or aliphatic hydrocarbon solution of the product.

[0029] As an alternative to polymerisation, the polymers may also be produced by transesterification. Thus, according to a second aspect of the present invention, there is provided a process for production the production of a polymer comprising the transesterification of at least one polymer of the ester (3) with an aliphatic alcohol or carboxylic acid having an aliphatic group of 4-40 carbon atoms.

[0030] Preferably, the alcohol or carboxylic acid has 4 to 30 carbon atoms, more preferably, 6 to 25 carbon atoms, even more preferably, 10 to 22 carbon atoms, preferably 6-16, and most preferably, 9-14 carbons, for example, 12 carbon atoms. Most preferably, an aliphatic alcohol is employed.

[0031] In one embodiment, a polyacrylate is transesterified with an alcohol having 4 to 40 carbon atoms. Preferably, the polyacrylate has a molecular weight of 1000 to 3000, more preferably, 1500 to 2500, for example, about 2000-2100. A suitable polyacrylate is polymethylacrylate. Most preferably, the polymethacrylate employed has a molecular weight of 1000 to 3000, more preferably, 1500 to 2500, for example, about 2000-2100.

[0032] The transesterified product may comprise 15 to 85% by weight, preferably, 55 to 75% by weight, more preferably, 60 to 70% by weight, for example, 60 to 65% by weight of units derived from the ester (3) polymer. The transesterified product may comprise 15 to 85% by weight, more preferably, 30 to 40% by weight, most preferably, 35 to 40% by weight of units derived from the alcohol or carboxylic acid. In one embodiment of the invention, the transesterified product comprises 60 to 63% by weight of units derived from the polymethacrylate and 37 to 40% of units derived from the alcohol or carboxylic acid. In a most preferred embodiment, the alcohol is a C12 or C16 alcohol.

[0033] The transesterification product of the invention may be purified, or used as such. In the case of the latter, the transesterification product may contain unreacted polymer and/or unreacted alcohol or acid. The unreacted alcohol or acid may be present in amount of 1-50%, for example, 10-50 % by weight, based on the weight of polymer (3). The unreacted alcohol or acid may optionally be removed.

[0034] The transesterification reaction may be performed at 50-150° C., for example, 60-120° C. The reaction time may be 1-30 hours, preferably, 5-20 hours.

[0035] A catalyst may be used to catalyse the transesterification reaction. Suitable catalysts include organic soluble strong acids and basic catalysts. Suitable acids include aromatic sulphuric acids, such as p-toluene sulphonic acid. Suitable basic catalysts include metal alkoxides. Suitable metal alkoxides include polyvalent metal alkoxides such as tetra methyl or tetra ethyl titanate, and alkali metal alkoxides such as sodium methoxide or ethoxide. Such alkoxides may be added as such or may be prepared in situ. Amounts of the basic catalyst may be 0.05-5% e.g. 0.1-1% by weight of the feed polymer.

[0036] The present invention also provides a method of reducing wax formation and/or deposition in a wax-containing middle distillate oil, said method comprising mixing a polymer of the present invention with said oil.

[0037] Preferably, said oil is mixed with a polymer of the present invention which is prepared using the transesterification process described above.

[0038] The middle distillate oil employed is typically a petroleum based oil obtainable from crude oil. Preferably, the middle distillate oil is obtainable as a fraction distilling in the lighter fuel oil (e.g. kerosene or jet fuel range) to the heavy fuel oil range (eg heating oil). Middle distillates may comprise atmospheric or vacuum distillates, cracked gas oil or blends of straight run and thermally and/or catalytically cracked distillates. Examples of suitable middle distillates include kerosene, jet fuel, diesel fuel, heating oil, visbroken gas oil, light cycle oil, vacuum gas oil, light fuel oil and fuel oil. The boiling range or the middle distillate measured (according to IP123/ASTM D86) is usually 100-500° C. eg 140-400° C. Diesel oil eg for vehicles which may be for summer or especially winter use, is preferred.

[0039] The middle distillate oil may comprise hydrocarbons which may be primarily aliphatic or aromatic in nature. Preferably, however, the oil comprises mixtures of aliphatic and aromatic hydrocarbons. The hydrocarbon may contain 0.01 to 30%, for example, 0.1 to 5% by weight of wax.

[0040] In the absence of the polymers of the invention, the middle distillate oil may have a cloud point value of at least −20° C., for example, −20 to 5° C., more specifically, −15 to 0° C. In certain embodiments, the middle distillate oil may have a cloud point of −15 to −5° C., for example, between −6 and −7° C. The polymers of the present invention may reduce the cloud point of the middle distillate oil by more than 0.2° C., preferably, more than 0.5° C., more preferably, more than 1° C., for example, between 0.2 and 3° C.

[0041] In the absence of the polymers of the invention, the pour point of the middle distillate oil may be 1-20° C., for example, 1-10° C. lower than the WAT (Wax Appearance Temperature) value. Thus, the pour point may be −30° C. to 0° C. e.g. −20° C. to −5° C. The polymers of the invention may reduce the pour point value of the liquid hydrocarbon by at least 3° C. e.g. 3-21° C. such as 6-15° C.

[0042] In the absence of the polymers of the present invention, the cold filter plugging point (CFPP) of the middle distillate oil may be at least −20° C., for example, 0 to −20° C., more specifically, −15 to −5° C., for example, −10 to −5° C. The polymers of the present invention may reduce the CFPP of the middle distillate oil by more than 0.5° C., preferably, more than 1° C., more preferably, more than 2° C., and most preferably, more than 3° C., for example, by 3 to 10° C.

[0043] The middle distillate oil may also contain at least one additive. Suitable additives include conventional flow improvers, such as a polyoxyalkylene compounds, ethylene vinyl acetate (EVA) copolymers, and nitrogenous compounds, preferably having at least one long chain such as of 4-40 carbons, hydrocarbyl bonded directly to nitrogen such as an amine salt or amide. Examples of suitable polyoxyalkylene compounds include polyoxyethylene diester, diether or ester/ether or mixtures thereof

[0044] Other suitable additives include detergents, anti foams, ignition improvers, lubricity additives and/or corrosion inhibitors. Mixtures of additives may be present in the middle distillate oil.

[0045] The polymer of the present invention may be added to the middle distillate oil, such that the final concentration of the polymer in the oil is 2-10,000, preferably, 5-10,000 ppm, more preferably, 10-8,000 ppm, even more preferably, 20-5000 ppm, yet more preferably, 50-1000 ppm. For example, the final concentration of the polymer in the oil may be 100 to 600 ppm, or more specifically, 250 to 500 ppm based on the weight of oil.

[0046] The polymer of the invention may be added to the middle distillate oil/middle distillate oil-containing mixture either batchwise, continually or continuously. For example, the polymer may be contacted with a moving liquid body of the oil, preferably, by adding the polymer to a line containing flowing liquid oil, upstream of a cooler location where wax deposition may occur in the absence of said compound. If desired the polymers of the invention may be added to a tank of the oil e.g. to inhibit deposition of wax.

[0047] It is possible to add the polymer directly to the middle distillate oil. Alternatively, the polymer may first be dissolved in a liquid solvent, and the resulting solution added to the middle distillate oil. Suitable solvents include hydrocarbon solvents such as toluene and/or xylene. The resulting solution may also comprise at least one of the aforementioned additives. The resulting solution or concentrate is such that each of the polymer and additive(s) is present in an amount of at least 1% e.g. at least 5% (by weight).

[0048] It has been found that when the polymers of the present invention are used in combination with certain additives, in particular, conventional flow improvers such as EVA, the activity of the additives is enhanced. Thus, according to yet another aspect of the present invention, there is provided a mixture comprising a middle distillate oil, a conventional flow improver and a polymer of the present invention. This mixture may be prepared by adding the polymer of the present invention to a mixture comprising a middle distillate oil and a conventional flow improver, or adding a conventional flow improver to a mixture comprising a middle distillate oil and the polymer of the present invention. Alternatively, the polymer of the present invention and the conventional flow improver may be added simultaneously to a middle distillate oil.

[0049] Suitable middle distillate oils, polymers of the present invention and conventional flow improvers include those described earlier in this specification. The preferred conventional flow improver employed is EVA. The preferred polymer of the present invention is one prepared by transesterification. Most preferably, this transesterified polymer is prepared by the transesterification of polymethacrylate and an alcohol. In one embodiment of the invention, the transesterified product comprises 60 to 63% by weight of units derived from the polymethacrylate and 37 to 40% of units derived from a C12 or C 16 alcohol. The starting polymethacrylate may have a molecular weight of 1500 to 3000, preferably, 2000 to 2500, for example, about 2100.

[0050] The amount of polymer present in the mixture of the present invention may be 2-10,000, preferably, 5-10,000 ppm, more preferably, 10-8,000 ppm, even more preferably, 20-5000 ppm, and yet more preferably, 50-1000 ppm. For example, the final concentration of the polymer in the oil may be 100 to 600 ppm, or more specifically, 250 to 500 ppm based on the weight of oil. The amount of conventional flow improver present may be 10-10,000 ppm, preferably, 20-5000 ppm, more preferably, 50-1000 ppm, even more preferably, 100 to 600 ppm, for example, 250 to 500 ppm based on the weight of oil. The mixture of the present invention may also contain 5-2000 ppm e.g. 30-1000 ppm (on the same basis) of medium chain alcohol, e.g. of 8-14 or 10-12 carbons, such as described for use in the preparation of the ester polymer.

[0051] Yet another aspect of the present invention is the use of a polymer as described above in a method for reducing at least one of the cloud point, CFPP and pour point of a middle distillate oil.

[0052] The present invention also provides the use of a polymer as described above for enhancing the flow characteristics (such as pour point, cloud point and/or cold filter plugging point (CFPP)) of a mixture comprising a middle distillate oil and a conventional flow improver, such as EVA.

[0053] The invention is illustrated in the following Examples:

EXAMPLE 1

[0054] A stirred solution of poly(methyl acrylate), M_(w) 2,100, (5.05g) and tetradecanol (7.55g) in toluene (100 ml), was heated in an oil bath at 130 C under Dean-Stark solvent removal conditions for 8 hours. Toluene (10 ml) was removed each 0.5 hr period and an equal amount of fresh toluene was replaced at that time.

[0055] After 1 hr sodium methoxide catalyst was added (47 mg). Extra sodium methoxide (95 mg). was added after another hour (total added =142 mg). The toluene solution of product, after cooling, was used as such is a 27% w/w solution.

[0056] Proton NMR spectroscopy indicated that the transesterification had proceeded to 77%, because of a 77:23 ratio of signals from the ester alkyl hydrogens to ester methyl hydrogens.

EXAMPLE 2

[0057] The procedure of Example 1 was followed with poly(methyl acrylate), MW 2,100, (5.04 g) and 1-dodecanol (6.49 g) and 165 mg of sodium methoxide was added in total. Proton NMR indicated a degree of transesterification of 84%.

EXAMPLE 3

[0058] The procedure of Example 1 was followed with poly(methyl acrylate), MW 2,100, (5.13 g) and Nafol 1618H (4.40 g). The sodium methoxide catalyst (94.5 mg) was added after 1.5 hours. The reaction was run for 10.5 hours. Proton NMR indicated a degree of transesterification of 38%.

EXAMPLE 4

[0059] The procedure of Example 1 was followed with poly(methyl acrylate), MW 2,100, (5.23 g) and 1-eicosanol (5.27 g). Xylene was used as the solvent instead of toluene. The reaction was run for 14.5 hours. After 1.5 hours sodium methoxide catalyst was added (0.118 g). Proton NMR indicated a degree of transesterification of 40%.

EXAMPLE 5

[0060] The procedure of Example 1 was followed with poly(methyl acrylate), MW 2,100, (5.17 g) and 1-docosanol (5.71 g). Xylene was used as the solvent instead of toluene. The reaction was run for 14.5 hours. After 1.5 hours sodium methoxide catalyst was added (0.118 g). Proton NMR indicated a degree of transesterification of 42%.

EXAMPLE 6

[0061] The procedure of Example 1 was followed with poly(methyl acrylate), MW 2,100, (3.08g) and 1-docosanol (6.66 g). Xylene was used as the solvent instead of toluene. The reaction was run for 10 hours. After 1.25 hours sodium methoxide catalyst (47 mg) was added. Additional sodium methoxide (71 mg) was added another 1.45 hours later. 1H NMR indicated a degree of transesterification of 83%. There was 6% of the initial 1-docosanol left unreacted.

EXAMPLE 7

[0062] A stirred solution of poly(methyl acrylate), MW 2,100, (5.09 g) and 1-dodecanol (3.21 g) in 100 ml of toluene was heated in an oil bath to 130 C with water and methanol removal using 4A molecular sieves for 9 hours.

[0063] After 2 hours sodium methoxide catalyst (0.1 18 g) was added. The toluene solution of product, after cooling, was used as such is a 15% w/w solution.

[0064] Proton NMR spectroscopy indicated that the transesterification had proceeded to 37%, because of a 37:63 ratio of signals from the ester alkyl hydrogens to ester methyl hydrogens.

EXAMPLE 8

[0065] The procedure of Example 7 was followed with poly(methyl acrylate), MW 2,100, (5.08 g) and 1-hexdecanol (4.30 g) and sodium methoxide (142 mg). The reaction was run for 9 hours. Proton NMR spectroscopy indicated a degree of transesterification of 40%.

EXAMPLE 9

[0066] The procedure of Example 7 was followed with poly(methyl acrylate), MW 2,100, (5.08 g) and 1-octadecanol (4.80 g). The reaction was run for 9 hours and 142 mg of sodium methoxide catalyst was used in total. Proton NMR indicated a degree of transesterification of 40%.

EXAMPLE 10

[0067] The procedure of Example 7 was followed with poly(methyl acrylate), MV 2,100, (5.08g) and 1-tetradecanol (3.81 g). The reaction was run for 8 hours. 1 hour into the reaction sodium methoxide catalyst was added (47 mg). After another hour a second portion of sodium methoxide catalyst (47 mg) was added. 1H NMR indicated a degree of transesterification of 37%. The product was present at 17% w/w in toluene.

EXAMPLE 11

[0068] The cloud point and CFPP of a middle distillate oil (commercial ultra low sulphur diesel grade) having the characteristics in Table 1 below were measured using IP 219/ASTM D2500 and IP 309, respectively. The cloud point was found to be −6.5° C., and the CFPP, −9° C.

[0069] The polymer produced in Example 7 was then added to the middle distillate oil of Table 1, such that the amount of polymer in the resulting mixture was 500 ppm. The cloud point and CFPP of the resulting mixture were −7.5 and −17° C., respectively.

[0070] It can be seen from this Example that the polymer of the present invention can be used to improve the cloud point and CFPP characteristics of a middle distillate oil. TABLE 1 Density 0.84 kg/m³ Initial Boiling point 200° C. Final boiling Point 350° C.

EXAMPLE 12

[0071] In this Example, the polymer produced in Example 7 and EVA were added to the middle distillate of Table 1, such that the resulting mixture contained 500 ppm of the polymer of Example 7 and 250 ppm of EVA. The CFPP of the resulting mixture was found to be −27° C.

[0072] It can be seen from this Example that when EVA and the polymer of Example 7 are added to a middle distillate oil, the CFPP of the middle distillate oil is decreased from −9° C. to −27° C.

COMPARATIVE EXAMPLE A

[0073] EVA was added to a heating oil in the proportions described in Table 2 below, and the CFPPs of the resulting mixtures were measured. The heating oil employed had a density of 0.845 g/cm³, a cloud point of 0.4, an initial boiling point of 170° C., and a final boiling point of 387° C. TABLE 2 EVA/ppm 100 200 400 600 CFPP/° C. −7 −9 −11 −11

EXAMPLE 13

[0074] In this Example, the polymer produced in Example 7 was added to the mixtures of Comparative Example A, in an amount of 5% of the amount of EVA already present in each of the respective mixtures. The CFPPs of the resulting mixtures were measured (see Table 3). TABLE 3 EVA/ppm 100 200 400 600 Polymer of Ex. 7/ppm 5 10 20 30 CFPP/° C. −16 −16 −18 −18

EXAMPLE 14

[0075] In this Example, a blend of heating oil, EVA (100 ppm) and polymer of Example 7 (10 ppm) was prepared. The CFPP of the blend was found to be −16° C.

EXAMPLE 15

[0076] In this Example, a blend of heating oil, EVA (100 ppm) and polymer of Example 7 (40 ppm) was prepared. The CFPP of the blend was found to be −18° C. 

1. A polymer having structural units derived from an ester (1) of an aliphatic carboxylic acid with an aliphatic alcohol, wherein either the acid or the alcohol is ethylenically unsaturated and the other of the acid or alcohol has a medium length chain group of 4-40 carbon atoms; said polymer having a molecular weight of less than 30,000.
 2. A process for the production of the polymer of claim 1, said process comprising transesterification of a) at least one polymer of an ester of an aliphatic carboxylic acid and an aliphatic alcohol, wherein either said acid or said alcohol is ethylenically unsaturated and the other of said acid or alcohol has a short chain aliphatic group of 1-4 carbon atoms, with b) an aliphatic alcohol or carboxylic acid having an aliphatic group of 4-40 carbon atoms.
 3. A process as claimed in claim 2, wherein said at least one polymer of an ester of an aliphatic carboxylic acid and an aliphatic alcohol is a polyacrylate.
 4. A process as claimed in claim 3, wherein said polyacrylate is polymethacrylate.
 5. A process as claimed in claim 3 or 4, wherein the polyacrylate employed has a molecular weight of 1000 to 3000 prior to transesterification.
 6. A process as claimed in any one of claims 2 to 5, wherein said a) at least one polymer of an ester of an aliphatic carboxylic acid and an aliphatic alcohol is transesterified with an aliphatic alcohol having 6-16 carbons.
 7. A polymer obtainable by the process of any one of claims 2 to
 6. 8. A polymer as claimed in claim 7, which 60 to 63% by weight of units derived from polymethacrylate and 37 to 40% of units derived from a C12 to C16 alcohol.
 9. A method of reducing wax formation and/or deposition in a wax-containing middle distillate oil, said method comprising mixing a polymer as claimed in claim 7 or 8 with said oil.
 10. A method as claimed in claim 9, wherein the middle distillate oil selected from the group consisting of kerosene, jet fuel, diesel fuel, heating oil, visbroken gas oil, light cycle oil, vacuum gas oil, light fuel oil and fuel oil.
 11. A mixture comprising a middle distillate oil, a conventional flow improver and a polymer as claimed in claim 7 or
 8. 12. A mixture as claimed in claim 11, wherein said conventional flow improver comprises ethyl vinyl acetate.
 13. A mixture as claimed in claim 11 or 12, wherein the amount of polymer present in said mixture is 2-10,000 ppm.
 14. A mixture as claimed in any one of claims 11 to 13, wherein the amount of conventional flow improver present is 10-10,000 ppm.
 15. Use of a polymer as claimed in any one of claims 7 to 8, for reducing at least one of the cloud point, CFPP and pour point of a middle distillate oil.
 16. Use of a polymer as claimed in any one of claims 7 to 8, for reducing at least one of the cloud point, CFPP and pour point of a mixture comprising a middle distillate oil and a conventional flow improver.
 17. Use as claimed in claim 16, wherein said conventional flow improver comprises ethyl vinyl acetate. 